A wireless communication system typically consists of one or more base stations providing communications coverage over a service area to one or more Subscriber Units (SUs). Each SU, which may be stationary or moving within the service area, establishes wireless links with one or more base stations. Communications are transmitted by the base station to the SU on the forward link and communications are transmitted by the SU to the base station on a reverse link. The forward link and the reverse link are normally separated by a frequency which limits interference between transmitters and receivers.
Different radio frequency technologies may be used in a wireless communication system. One example is Code Division Multiple Access (CDMA). In typical CDMA systems, many users communicate over the same frequency channel with different communication links being identified by an unique set of modulation codes. For a given user, transmissions by other users appear as noise with respect to the given user's signal at the base station receiver. For the receiver to be able to successfully decode the transmission from a particular user, the intended signal must be of sufficient strength when compared to the "noise" from transmissions by other SUs. For this reason, the power level at which SUs transmit is very important.
CDMA systems are an example of wireless systems where it is important for each base stations to control the transmit power received from SUs communicating over reverse links. The means by which the base station controls the transmit power over reverse links is called Reverse Link Power Control, The goal of Reverse Link Power Control is to keep each SU transmitting at the absolute minimum power level necessary to ensure an acceptable service quality. The number of simultaneous users that the system can support depends greatly on how precisely the transmit power of all users can be maintained at ideal levels. If a SU transmits at excessive power, it increases the interference to the transmissions of other SUs. Transmission at higher than required levels also impacts negatively on the battery life of SUs.
The importance of Reverse Link Power Control is further exacerbated by high speed data (HSD) reverse links that use multiple code channels. For high speed data reverse links, several code channels are used simultaneously by a given SU to provide a high data rate. As the Reverse Link Power Control mechanism adjusts the transmit power on the reverse link, the power level of all code channels assigned to an SU change in unison. This increases the variance of the received power level at the receiver and this increase may cause a degradation in service quality as well as a negative impact on the system radio capacity.